Mapping Oil Spills

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Based on the article: Kheraj, Sean. “A History of Oil Spills on Long-Distance Pipelines in Canada.” The Canadian historical review 101, no. 2 (2020): 161–191,

Photo: Construction of the Interprovincial Pipeline. Retrieved from, “Concentrated Gravity Work in Ontario,” Financial Post, Nov. 24, 1951, P.50.

Onshore oil pipeline spills and leaks were a regular occurrence on the Interprovincial crude oil pipeline (now known as the “Enbridge Mainline”), and always have been, an incident report of the National Energy Board (NEB) reveals.[1]  The report, referenced below, from the regulatory agency counts a total of one-hundred-and-ninety oil spills in the period of 1962 to 1996. It, furthermore, provides partial answers to such questions as; what were the causes of Interprovincial’s recorded spills; how much oil has the line spilled over the years; and where have they occurred most? 

This article offers initial visualizations (graphs and diagrams) of the NEB dataset to help answer these questions. The dataset itself is attached as well. This page thereby hopes to function as a point of departure for anyone interested in the history of Canada’s oil pipeline spills. The visualizations help illustrate that spills on the Interprovincial Pipeline did not conform to an obvious pattern over time. Instead, its spills occurred most often in an unpredictable fashion, making it tough to formulate an effective policy response. 

The Line and its Spills

Currently, the Interprovincial pipeline is one of the largest oil pipeline systems in the world. It consists of various segments in Canada and the United States and runs from Edmonton to Montreal, crossing the Canadian provinces of Alberta, Saskatchewan, Manitoba, Ontario, and Quebec as well as the American states of North Dakota, Minnesota, Wisconsin, Illinois, Indiana, Michigan, and New York. Build in 1949, it has leaked oil, in every Canadian province it traversed, since its very start, as the following map reveals. 

The earliest spills remained largely unrecorded, but the National Energy Board has more reliably documented those that occurred after 1961. The NEB also documented what brought them about. An excel version of the Interprovincial Pipeline’s part of the incident report can be found below.


The NEB identified the diverse causes of most spills, albeit in a rather general fashion. “Hardware Failure” was listed most frequently as the cause of oil spills, forty-nine times. The details that operators added over the years to this type of failure reveal that the term “Hardware Failure” could mean anything from cracks in valves to failures of seals, and metal fatigue. In 1974, for instance, near Strome Alberta, a five-foot-long split along a longitudinal weld caused 4,452,000 liters of crude oil to flood an adjacent area of roughly 30,000 square-foot. In 1976, just outside of Killam, Alberta, 2,835,000 liters got past a faulty weld. During the clean-up operations, a fire broke out, killing two and injuring seven others.[2]

The second most common cause of spills was “miscellaneous,” “unknown,” “unknown by company” or unavailable causes (represented in the figure as “N/A”). Forty-three out of one-hundred-eighty-nine reports of these were made. That is nearly twenty-three percent. Both “Earth Movement” and “Weld Corrosion” caused the least number of spills. “Earth Movement” being frost heave inflicted damage and “Weld Corrosion,” according to the NEB incident report, meaning, “two pinhole leaks on a welding bar.” The causes thus varied and the NEB document hints as to what could have happened.     

In hindside, some oil spills could perhaps have been prevented. Prior to the line’s opening in 1950, the company did not conduct hydrostatic pressure testing.[3] Instead, the national Board of Transport Commissioners, which oversees a range of transportation concerns, allowed Interprovincial to skip the tests with water and test the line with oil instead. This resulted in at least two oil spills between Edmonton and Superior. After the opening of the line, farmers along the right of way discovered various other spills and leaks. The Globe and Mail reported that in November 1950, Interprovincial spilled roughly 31,797 litres of crude oil in a farmer’s field in Minnesota. A few months later, in early 1951, another major leak took place when a contractor’s equipment accidentally damaged the line in North Dakota.[3] These spills could, arguably, have been prevented in some shape or form. 

 Spill Frequency and Quantity

However, oil spills primarily remained unpredictable. The following diagram illustrates that many spills occurred in the 1970s, during the peak of Interprovincial’s expansion. Between 1973 and 1975, the company encountered what one newspaper report labelled “an unusually high spill rate.”[5] According to the NEB’s incident data, the company reported twenty-four oil spills, totaling nearly eleven million litres spilled into the environment between 1973 and 1975. This worried both the authorities on a federal and provincial level. In Alberta, the series of substantial spills in January 1974 in the Strome area, especially troubled the province’s environment minister, Bill Yurko.[6]

Between 1962 to 1996, the year 1967 was Interprovincial’s worst. In that year, the company delivered approximately thirty-seven billion litres of liquid hydrocarbons and they spilled 11,081,500 litres of oil. In total over the course of its history from 1962 to 1987, Interprovincial lost 0.003 percent of the total volume of liquid hydrocarbon deliveries. Despite all the oil spilled, it was thus still more than ninety-nine percent successful. The small fraction of spills, however, in reality, meant that more than forty-one million litres spilled. Between 1962 and 1996, Interprovincial reported a total of one-hundred-ninety oil spills. This meant that Interprovincial’s annual spill rate during this period was 5.43 spills a year. 

 Spill Locations

These litres of oils were mostly spilled in rural communities made up of both settler farmers and Indigenous peoples. Urban areas were rarely subjected to oil spills as onshore spills occurred mostly in rural areas along the right-of-way or at remote tank farms and pump stations. Sixty-seven percent (the majority) of oil spills happened near pump station sand other Interprovincial facilities, but the mainline spills tended to be more substantial. Mainline spills accounted for seventy-seven percent of all oil spilled between 1962 and 1996. Those who lived in these regions often struggled to challenge the large, foreign-owned Interprovincial pipeline corporation. Without effective resistance, Interprovincial continued to accept a number of pipeline failures.[7]

 On the NEB Incident Report

Since 1961, the NEB has required Interprovincial to provide reports on a range of incident types, including oil spills. The NEB keeps these reports in a large database that also contains occurrences that are not spills and incidents on other pipelines. 

The information in this article largely comes from the NEB’s incident report, which covers the period 1961 to 1996. The incident report has its flaws. For starters, any incidents that occurred prior to 1961 remain unrecorded. Alternative records like newspaper sources or public accounts offer some insight into these but conducting a systematic analysis at a level that is comparable to the cases post-1961 is impossible. Secondly, many small incidents, likely, went unreported. For the post-1961 period, the information available is wide-ranging. Thirty-four fields make up the incident report, ranging from “type of incident,” to “causes,” and “quantity of product spilled.” The report also contains a field labelled, “other.” This category contains valuable insights for more qualitative analysis. The information is helpful but leaves much to be desired. The main flaw of the incident report is thereby missing information. 

The original NEB spill report can be found here.

[1] The National Energy Board (NEB) is the Canadian regulatory body that oversees energy infrastructure that crosses interprovincial and national boundaries. 

[2] Sean Kheraj, “A History of Oil Spills on Long-Distance Pipelines in Canada.” The Canadian historical review 101, no. 2 (2020): P. 187-188,

[3] A hydrostatic test is a test of a pipeline with water. In a hydrostatic test, there is residual oil in the line. When there is a spill during a hydrostatic test, the residual oil spills along with the water. 

[4] Sean Kheraj, P.184.

[5] Ibid., P.187. 

[6] Ibid., P.187. 

[7] Ibid., P.165, 167.